Catalytic Conversion of Ethanol and Hydrogen to a 1-Butanol-Containing Reaction Product Using a Thermally Decomposed Hydrotalcite/Metal Carbonate

ABSTRACT

Hydrotalcite/metal carbonate combinations are partially or fully thermally decomposed to provide catalysts useful for the conversion of ethanol and hydrogen to a reaction product comprising 1-butanol.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims benefit of priority from Provisional ApplicationNo. 61/062,604, filed Jan. 28, 2008.

FIELD OF THE INVENTION

The present invention relates to the catalytic conversion of ethanol andhydrogen to a 1-butanol-containing reaction product. Various organicchemicals, including 1-butanol itself, can be separated from thereaction product. The catalysts are combinations of hydrotalcites(optionally containing transition metals) and metal carbonates, whichcombinations have been thermally decomposed, either partially or fully,to form catalytically active species.

BACKGROUND

Efforts directed at improving air quality and increasing energyproduction from renewable resources have resulted in renewed interest inalternative fuels, such as ethanol and butanol, that might replacegasoline and diesel fuel, or be used as additives in gasoline and dieselfuel.

It is known that 1-butanol can be prepared by condensation from ethanolover basic catalysts at high temperature using the so-called “GuerbetReaction.” See for example, J. Logsdon in Kirk-Othmer Encyclopedia ofChemical Technology, John Wiley and Sons, Inc., New York, 2001.

Methods of using catalysts to convert ethanol to butanol are alsodiscussed in the following references.

M. N. Dvornikoff and M. W. Farrar, J. of Organic Chemistry (1957), 11,540-542, disclose the use of MgO-K₂CO₃—CuCrO₂ catalyst system to promoteethanol condensation to higher alcohols, including 1-butanol. Thedisclosed liquid phase reaction using this catalyst showed a 13%conversion of ethanol and 47% selectivity to 1-butanol.

U.S. Pat. No. 5,300,695, assigned to Amoco Corp., discloses processes inwhich an alcohol having X carbon atoms is reacted over an L-type zeolitecatalyst to produce a higher molecular weight alcohol. In someembodiments, a first alcohol having X carbon atoms is condensed with asecond alcohol having Y carbon atoms to produce an alcohol having X+Ycarbons. In one specific embodiment, ethanol is used to produce butanolusing a potassium L-type zeolite.

J. I. DiCosimo, et al., in Journal of Catalysis (2000), 190(2), 261-275,describe the effect of composition and surface properties onalcohol-coupling reactions using Mg_(y)AIO_(x) catalysts for alcoholreactions, including ethanol. Also condensation reactions onMg_(y)AIO_(x) samples involved the formation of products containing anew C—C bond, such as n-C₄H₈O (or n-C₄H₉OH) and iso-C₄H₈O (oriso-C₄H₉OH). They also describe, in Journal of Catalysis (1998), 178(2),499-510, that the oxidation to acetaldehyde and the aldol condensationto n-butanol both involve initial surface ethoxide formation on a Lewisacid-strong base pair.

WO 2006059729 (assigned to Kabushiki Kaisha Sangi) describes a processfor efficiently producing, from ethanol as a raw material, highermolecular weight alcohols having an even number of carbon atoms, such as1-butanol, hexanol and the like. The higher molecular weight alcoholsare yielded from ethanol as a starting material with the aid of acalcium phosphate compound, e.g., hydroxyapatite Ca₁₀(PO₄)₆(OH)₂,tricalcium phosphate Ca₈(PO₄)₂, calcium monohydrogen phosphateCaHPO₄×(0-2)H₂O, calcium diphosphate Ca₂P₂O₇, octacalcium phosphateCa₈H₂(PO₄)₆×5H₂O, tetracalcium phosphate Ca₄(PO₄)₂O, or amorphouscalcium phosphate Ca₃(PO₄)₂×nH₂O, preferably hydroxyapatite, as acatalyst, the contact time being 0.4 second or longer.

Carlini et al. describe a catalytic reaction of methanol with n-propanolto produce isobutyl alcohol. The involved catalyst is a calcinedhydrotalcite in combination with copper chromite. See C. Carlini et al,Journal of Molecular Catalysis A: Chemical (2005), 232 (1-2) 13-20. Seealso C. Carlini, Journal of Molecular Catalysis A: Chemical (2004), 220(2), 215-220, in which the catalyst is a mixture of a hydrotalcite withPd, Ni, Rh, or Cu, with the mixture being calcined at 500° C.

Hydrotalcites are layered, double hydroxides of the general formula

(M²⁺ _(1−x)M³⁺ _(x)(OH)₂)(A^(n−) _(x/n)).yH₂O

The M²⁺ ions can be a variety of divalent cations (e.g., Mg, Ni, Pt, Pd,Zn, Co, Fe, Cu) and the M³⁺ ions can be trivalent Al, Fe or Cr. Somehydrotalcites are described by V. K. Diez, C. R. Apesteguia, and J. I.DiCosimo (Latin American Applied Research, 33, 79-86 (2003)) and N,N.Das and S. C. Srivastava (Bull. Mater. Sci. 25, (4), 283-289 (2002)).

It has been found that partially or fully thermally decomposedcombinations of hydrotalcites (particularly those that incorporatetransition metals) and metal carbonates can yield catalysts that areeffective for the conversion of ethanol and hydrogen to a reactionproduct that comprises (i.e., contains, among other things) 1-butanol.

SUMMARY OF THE INVENTION

Certain combinations of hydrotalcites and metal carbonates, as describedherein, are partially or fully thermally decomposed to provide catalystsuseful for the conversion of ethanol, in the presence of hydrogen, to areaction product comprising 1-butanol.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 shows the powder X-ray diffraction pattern of the hydrotalcitematerial of the Examples before calcination, and indicates reflectionstypical of a hydrotalcite phase.

FIG. 2 shows a powder X-ray diffraction pattern of the material of FIG.1 after calcination, showing decomposition of the hydrotalcite phase bythe substantial loss of those reflections that are typical of ahydrotalcite phase.

DESCRIPTION

A stream of gas phase ethanol (that may contain water, and may bediluted with an inert gas such as nitrogen, carbon dioxide, and mixturesthereof) is contacted in the presence of hydrogen with at least onethermally decomposed hydrotalcite catalyst at a temperature and pressuresufficient to produce a reaction product comprising water, unreactedethanol (if less than complete ethanol conversion), butanol, higheralcohols and other organic species. The butanol is predominantly1-butanol. Suitable temperatures are in the range of about 150° C. to500° C., for example about 200° C. to about 500° C. Suitable pressuresare from about 0.1 MPa to about 20.7 MPa. Hydrogen is supplied to thereactor at a feed rate of at least 5 percent by volume relative to thevolume of feed gas.

The catalysts that are useful in the present invention are partially orfully thermally decomposed hydrotalcite/metal carbonate combinations ofa hydrotalcite of the formula [(M²⁺ _(1−x)M³⁺ _(x)(OH)₂) (A^(n−)_(x/n)).yH₂O] and a metal carbonate of the formula [M′A′]. Thecombinations, prior to thermal decomposition, have the empirical formulabelow:

[[(M²⁺ _(1−x)M³⁺ _(x)(OH)₂)(A^(n−) _(x/n))].yH₂O][M′A′]_(z)

whereinM²⁺ is divalent Mg, or a combination of Mg and at least one divalentmember selected from the group consisting of Pd, Pt, Co and Cu; M³⁺ istrivalent Al, or a combination of trivalent Al and at least onetrivalent member selected from the group consisting of Fe and Cr;

-   x is 0.66 to 0.1;-   A^(n−) is CO₃ ²⁻ with n=2, or OH⁻ with n=1;-   M′A′ is a carbonate of at least one divalent metal M′ selected from    the group consisting of Pd, Pt, Co and Cu; and A′ is carbonate;-   z is any number between 0.001 and 0.5, inclusive (i.e., including    the endpoints of the range); and-   y is 0 to 4.

In a preferred embodiment of this invention, in the empirical formulaM²⁺ is divalent Mg; M³⁺ is trivalent Al; A^(n−) is CO₃ ²⁻ or OH⁻; z isany number between 0.001 and 0.5; and M′ is selected from the groupconsisting of Pd, Pt, Co and Cu. Preferred values for M′ are Co and Cu.Preferred values for z are in the range between 0.01 and 0.25, includingthe endpoints of the range.

The catalysts that are useful in the present invention are derived froma hydrotalcite of the formula as defined above by a process comprisingheating the hydrotalcite for a time and at a temperature sufficient tocause a diminution in the hydrotalcite powder X-ray diffraction patternpeak intensities between 2θ angles of 10 degrees and 70 degrees usingCuKα radiation.

Catalysts derived from the hydrotalcite can be synthesized by thefollowing method. An aqueous salt solution containing (a) magnesium andone or more divalent metals selected from the group consisting ofpalladium, platinum, cobalt and copper and (b) aluminum and, optionally,one or more trivalent metals selected from the group consisting of ironand chromium is prepared. Preferred salts are nitrates, chlorides, oracetates. Most preferred are nitrates. The salt solution is added to abasic, aqueous solution containing sodium or potassium carbonate (orbicarbonate), sodium, potassium or ammonium hydroxide, or a mixture ofthe foregoing carbonates, bicarbonates and hydroxides, thereby providingthe carbonate ion or hydroxide ion for A^(n−), as well as the carbonateion for A′. The pH of this basic solution is typically adjusted to a pHof approximately 10 during the addition of the aqueous salt solution.The (a) magnesium and at least one other divalent metal and the (b)aluminum and optional trivalent metals should be in a molar ratio(a)/(b) between 0.5 and 9 inclusive (i.e., including the endpoints ofthe range) to satisfy the stoichiometry of the hydrotalcite component ofthe formula (I). In practice, however, the endpoints of the range shouldexceed 0.5 and 9 by an amount sufficient to satisfy the value of “z” forthe [M′A′] component of formula (I). This is because the metal M′ isselected from the same group of metals as the metals that can substitutefor divalent magnesium in the hydrotalcite component of formula (I).(Alternatively, a plurality of individual metal salt solutions may beused, provided that they are added concurrently to the basic, aqueoussolution containing the carbonate, bicarbonate, hydroxide or mixturesthereof.)

The resulting suspension that is formed (i.e., a precipitate suspendedin a liquid) can be aged, preferably for approximately 18 hours, atabout 60° C. to 70° C. The precipitate is then separated, generally byfiltering, and subsequently dried (generally in a vacuum oven or inair). The dried precipitate can be analyzed by powder X-ray diffractionto confirm the presence of a hydrotalcite phase. This phase isisostructural with the hydrotalcite Mg₆Al₂(CO₃)(OH)₁₆.4H₂O(JCPDS card #54-1030; Powder Diffraction Files, International Centre for DiffractionData, 1601 Park Lane, Swarthmore, Pa. 19081). The dried precipitate isthen calcined by heating it for a time and at a temperature sufficientto cause a diminution in the hydrotalcite powder X-ray diffractionpattern peak intensities between 2θ angles of 10 degrees and 70 degreesusing CuKα radiation. The calcined material can be analyzed by powderX-ray diffraction to confirm the diminution (including the completeabsence) in these peak intensities and the appearance of new peakscorresponding to a material which is isostructural with partiallycrystalline magnesium oxide (MgO, JCPDS card # 65-0476). It is preferredto calcine the dried precipitate for a time and at a temperaturesufficient to substantially reduce the peak intensities characteristicof the hydrotalcite phase.

Although any calcination protocol can be used, one that is particularlyuseful on a laboratory scale includes heating the hydrotalcite in a 2.5centimeter (cm) (one inch) diameter tube furnace from about 25° C. toabout 360° C. over 140 minutes (min) at 2.4° C. per minute, and thenholding at 360° C. for about 2 to about 4 hours.

The catalysts usable in the process of the invention can be prepared asdescribed above. The catalysts may be used in the form of powders,granules, or other particulate forms. Selection of an optimal averageparticle size for the catalyst will depend upon such process parametersas reactor residence time and desired reactor flow rates.

The catalytic conversion of ethanol and hydrogen to the reaction productcomprising 1-butanol can be run in either batch or continuous mode asdescribed, for example, in H. Scott Fogler, (Elements of ChemicalReaction Engineering, 2^(nd) Edition, (1992) Prentice-Hall Inc, CA).Suitable reactors include fixed-bed, adiabatic, fluid-bed, transportbed, and moving bed.

It is preferable, but not essential, to treat the catalyst, prior to itsuse, with nitrogen or air at elevated temperatures, which is thought toremove unwanted carbonates from the catalyst surface. If the startinghydrotalcite contains Pd, Pt, Co or Cu, it is also preferred, but notessential, to treat the catalyst, prior to its use, with hydrogen atelevated temperatures. One protocol that has been found to be effectiveis described in more detail in the Example, below. If catalyst treatmentis desired, the catalyst may be treated in situ in the reactor or exsitu and then introduced into the reactor.

During the course of the reaction, the catalyst may become fouled, andtherefore it may be necessary to regenerate the catalyst. Preferredmethods of catalyst regeneration include contacting the catalyst with agas such as, but not limited to, air, steam, hydrogen, nitrogen orcombinations thereof, at an elevated temperature, although care must betaken not to use a temperature that is so high that the regenerationresults in a loss of surface area or other unwanted effects. If catalystregeneration is desired, the catalyst may be regenerated in situ in thereactor or ex situ and then introduced into the reactor.

One skilled in the art will know that conditions, such as temperature,catalytic metal, catalyst support, reactor configuration and time canaffect the reaction kinetics, product yield and product selectivity.Standard experimentation can be used to optimize the yield of 1-butanolfrom the reaction.

1-Butanol can be separated from the reaction product by known chemicalengineering methods, including distillation. Other specific chemicals(or combinations of chemicals) also can be removed from the reactionproduct using known chemical engineering methods. The specific methodswill be dependent on the nature of the reaction product, which, in turn,is dependent on the specific catalyst used and the reaction conditions,particularly the extent of ethanol conversion.

EXAMPLES Examples 1-2 [(M²⁺ _(1−x)M³⁺ _(x)(OH)₂)(A^(n−)_(x/n))].yH₂O][M′A′]_(z) hydrotalcite M²⁺ is Mg; M³⁺ is Al; x is 0.25;A^(n−) is CO₃ ²⁻ with n=2; M′ is Cu²⁺; A′ is CO₃ ²⁻; z=0.013; and y=0 to4

Examples 1-2 are comparative examples carried out at 300° C. and 350°C., respectively, under a flow of nitrogen. Sodium bicarbonate (8.2 g;EMD Sciences, Gibbstown N.J.) was dissolved in 250 milliliters (ml)water in a three neck, round bottom flask. The solution was heated to65° C., and the pH was adjusted to approximately 10 using 2 M sodiumhydroxide solution (Baker). 27.5 g of aluminum nitrate(Al(NO₃)₃.9H₂O(EMD Sciences AX0705-11)), 57.6 g of magnesium nitrate(Mg(NO₃)₂.6H₂O (EMD Sciences MX0060-1)) and 0.92 g of copper nitrate(Cu(NO₃)₂. 2.5H₂O(Fisher, Lot#725840)) were dissolved in 100 ml of waterand added drop-wise to the preheated solution containing sodiumbicarbonate. After complete addition of the metal nitrates, thesuspension was kept at 65° C. with stirring for 1 hour (hr) and thenaged at this temperature for 18 hours without stirring.

The precipitate was separated from solution by filtering. Theprecipitate was dried in a vacuum oven at 90° C. for 48 hrs and calcinedat 360° C. for 2 hours in nitrogen. The heating protocol was as follows:the precipitate was placed in a 2.5 cm (1 inch) diameter tube furnace,and the temperature was raised from 25° C. to 360° C. at 2.4° C./minuteover 140 minutes, and held at 360° C. for 2 hours.

The catalyst was evaluated according to the following procedure.

Reactor Evaluation:

Approximately 2 cubic centimeters (cc) of catalyst was loaded on astainless steel mesh support within a 45.7 cm×1.3 cm (18 inch x ½ inch)outside diameter (o.d.) type 360 stainless steel tube reactor withinlets for gas and liquid feeds. The catalyst was then pre-conditionedin situ by flowing nitrogen gas, initially at room temperature, raisingthe temperature to 350° C., holding it there for one hour, lowering thetemperature to 180° C., flowing hydrogen gas at 15 cc/min for one hour,reintroducing nitrogen gas at a flow rate of 15 cc/min, and increasingthe reactor temperature to that shown in Table 1 to introduce theethanol to generate reaction data. At reaction temperature, nitrogenflow was set at 15 cc/min and ethanol flow at 1.03 ml/hr. The majorityof the reaction off-gases were condensed throughout a 60 minute reactiontime in cold N-methylpyrrolidone solvent, and the resultant solution wasanalyzed using an Agilent™ 5890 GC equipped with flame ionization andmass selective detectors. Results are shown in Table 1 below, wherein“EtOH” means ethanol, “BuOH” means 1-butanol, “Conv.” means conversion,and “Sel.” means selectivity. Ethanol conversion (%) was calculated asfollows: [(1-carbon moles of unreacted ethanol)/carbon moles of totaloutlet gases] times 100. Selectivity (%) was calculated as follows:(carbon moles of product/carbon moles of ethanol reacted) times 100.

TABLE 1 Example Temp. EtOH BuOH Butanol No. ° C. Minutes Gas Conv. Sel.Yield 1 300 60 N₂ 10.3 27.2 2.8 2 350 60 N₂ 10.6 40.6 4.3

Examples 3-4 [(M²⁺ _(1−x)M³⁺ _(x)(OH)₂)(A^(n−) _(x/n))].yH₂O][M′A′]_(z)hydrotalcite M²⁺ is Mg; M³⁺ is Al; x is 0.25; A^(n−) is CO₃ ²⁻ with n=2;M′ is CU²⁺; A′ is CO₃ ²⁻; z=0.013; and y=0 to 4

The catalyst was prepared and evaluated according to the proceduredescribed in Examples 1-2, except that the gas flow used in the reactorevaluation reaction with ethanol was hydrogen instead of nitrogen. Theresults are shown in Table 2.

TABLE 2 Example Temp. EtOH BuOH Butanol No. ° C. Minutes Gas Conv. Sel.Yield 3 300 60 H₂ 27.6 19.3 5.3 4 350 60 H₂ 25.7 19.1 4.9

Although particular embodiments of the present invention have beendescribed in the foregoing description, it will be understood by thoseskilled in the art that the invention is capable of numerousmodifications, substitutions, and rearrangements without departing fromthe spirit or essential attributes of the invention. Reference should bemade to the appended claims, rather than to the foregoing specification,as indicating the scope of the invention.

1. A process for making a reaction product comprising 1-butanol,comprising: contacting a reactant comprising ethanol and hydrogen with acatalyst at a reaction temperature and pressure sufficient to producesaid reaction product, wherein said catalyst is derived from ahydrotalcite of the formula:[[M₂₊ _(1−x)M³⁺ _(x)(OH)₂)(A^(n−) _(x/n))].yH₂O][M′A′]_(z) wherein M²⁺is divalent Mg, or a combination of Mg and at least one divalent memberselected from the group consisting of Pd, Pt, Co and Cu; M³⁺ istrivalent Al, or a combination of trivalent Al and at least onetrivalent member selected from the group consisting of Fe and Cr; x is0.66 to 0.1; A^(n−) is CO₃ ²⁻ with n=2, or OH⁻ with n=1; M′A′ is acarbonate of at least one divalent metal M′ selected from the groupconsisting of Pd, Pt, Co and Cu; and A′ is carbonate; z is any numberbetween 0.001 and 0.5 inclusive; and y is 0 to 4, by a processcomprising heating the hydrotalcite for a time and at a temperaturesufficient to cause a diminution in the hydrotalcite powder X-raydiffraction pattern peak intensities between 2θ angles of 10 degrees and70 degrees using CuKα radiation.
 2. The process of claim 1, wherein M²⁺is divalent Mg; M³⁺ is trivalent Al; and A^(n−) is CO₃ ²⁻ or OH⁻.
 3. Theprocess of claim 1, wherein said reaction temperature is from about 200°C. to about 500° C., and said pressure is from about 0.1 MPa to about20.7 MPa.